Air dashpot



April 11, 1933.

F. G. 1 BOYER AIR DASHPOT Original Filed Feb. 2. 1925 IN1/Emo.

` f BY //K f ATTORNEYS.

Patented Apr. 11, 1933 i fuNiTED ,STATES P OEE Frtuinierenci.` L. BOYERQOF DAyTomoHIo a AIR DASHPOT original application mea February 2, 1923,seria1 No. aia-50a mviaednand this' applicati@ inea "January 23,1925. semi 1ro.`4,347.

My invention relates to that type of devices known as dash pots, and has for its object thepr-ovisionnof a form of ldash pot which will combine certain important advantages of 5 both air and liquid dash pots and eliminate certain disadvantages of both types., InairV dash pots, as is well known, the resistance increases very rapidly as the piston approaches the closed end of the cylinder. In som-e cases lothis is adesirable feature, but in other cases it is such a serious disadvantage as to compel the rabandonment of an air dash p-ot and the use'of one containing liquid. On the other l hand, if a liquid dash pot is used inorder to Y obtain uniform resistance throughout the length of the stroke, it`will be found that the changes in viscosity of the liquid used, dueto temperature changes, will produce'objection-.-

able changes in the resistance. Furthermore it is often found difficult to prevent leakageif oil or other liquid is used, especially if the piston must move sofreely that a stuffing box may not be used. l

' These and other seri-ous objections to both air and liquid dash pots as now made are overcome by my invention in which I use air to avoid the disadvantages inherent'in liquid dash pots, and provide certain novel means to overcome the above mentioned disadvantage 3o of an air dash pot. To do this I providethat, as the piston is forced into the dash pot, at the point Where the resistance has reached the 4desired strength the inside diameter of the cylinder begins to gradually increase ,to-

wards the closed end. This provides a greaterrelief as the pressure tends to become greater, thus comparatively equalizing the resistance throughout the length of the dash i pot, or as great a portion of the length as de- 40 sired. A

One type of device on which dash pots of this type are particularly useful is shown in my co-pending application Serial No. 616,509, filed Feb. 2, 1923, from which application the '4 present application is a division.

The construction and operation will be bett-er understood by reference to the accomf panying drawing in which Fig. 1 shows one form of dash pot embodying my invention.

kgreat as to befobjectionable in'many: cases. In order to provide this'relief I provide-.foral Y simple form of air dashfpot embodying invention. The single cylinder 11is openA at itsllower end andclosed at its upper ,endg

by 2i Plugf12 screwed into the end Ofthicyl;

inder, or 1n any other manner desired. y'The piston 13 is made longer than its diameterinvv order to make it self-guiding and to decrease* the amount of `*leakage between .piston and* cylinder. A screw 14 is used 'to attach a .cle v"l is l5 to ,thepis'ton 13, becauseas will presently be described, the piston mayfbe made of a material such that the clevis cou'ldynot; Y conveniently be formed integralnwith pin 16 i's used toattach this clevis'fto a pitman or connecting rod 17 which lconnects-itt() the#r machine partwhose speed it isidesired 'toV retard. A port 18 is rovided in the cylinder just abovethe top oI the ipiston at its lowestf position, shown in'brokenlines -at 13-`L;inf* Fig. This relieves the suction vabovethel piston which might otherwise nullify, to` a" large extent, the'retardingeflect Von theu'p#y Award stroke.l V g 4As soon asthe upwardv stroke ofthe lpiston begins the air pressure above it increasesrapf idly, and if there wereno means of relieving v this pressure as the piston `approaches the closed'end of the cylinder,.itwould soon' be soi gradually increasing the internal diameter of the cylinder after the piston reaches the point, shown las '19 in Fig. 1, where-thepressure be? hind ithas reached the degreefde'sired. 'The taper is madeA of theidegree which ,Willgiv'ef theamount of'relief desired on theparticular device'onlwhich theldash vp otis tome-used. In order to make its action lapproximate'that of aliquid dash potthe taper is made of such a degree esito' make the resistant'ze` appro'ii-UL matelyfuniform after it `reaches thefd'esiredintensity.V The degree oftaper shown on the 5 drawing is much 'exaggerated in order that it." maybe more-easily di'stinguished` 4If it iS obtained with an ordinary air dash pot) greater relief may be provided for this purpose near the end.

In order that the action of this dash pot shall be as nearly uniform as possible at all times, it is desirable that it -should always operate dry, and that no oil should ever be used Y between the piston and cylinder. This is true not `only `because'oil tends to dry, become gu'nmy" and cause the piston to stick, if n otv kept fresh, but also because oil aroundV the piston tends to form an air seal which would nullify the effect of the increasinginternal diameter until the sealwould break because ofthe larger clearance and increasing air 29 pressure, or because of the decrease in the amount of oil with continued use of the device. vIn yorder to overcome this disadvantage I find it advisable to make the piston of a material which will Work without .the addi- ,25. 4tion of oil or other lubricant. Various materials of this kind are now on the market and usedfor the construction of oilless bearings, and usually consist ofwood, metal, and other material impregnated with waX,-ooil, or some 3Q n, other form of lubricant.

In Fig. 2 is illustrated a dash pot comprising'acylinder 21 closed by a plug 22 and pro- .videdwith a port 28, just as is the dash pot illustrated in Fig. l. In this case the piston 35. is of a slightly vdifferent form, having annular grooves 23-A which tend to prevent leakage of air around the piston, and which may be provided if desired. The piston is connected, as before, by means of` a connecting @rod 27 to a machine part whose motion it is desired to control, which is shown as a manually or otherwise operatedlever 40 mounted to rock on a center 41 and adapted to be returned to position by a spring 42.

4?; In thiscase ,it may be necessary, in order to produce an approximately uniform retarding eiiect throughout the length of the stroke, to provide a greater relief as the piston approaches the closed end of the cylinder, in

59order to regulate thefresistance to the progressively decreasing power 4of the spring.

V.Whenmy improved dash pot is used on a device such as that indicated in Fig..2 and more fully described in my co-pending ap- .55,plication above mentioned, the effect of the resistance as the piston moves away from the closedend of the cylinder is'of less imp ortance than that when it is moving in the opposite direction; but it should be noted, in

69 ,case it should be desired to use my dash'pot where'the resistance on both strokes is of importance, that the tapered cylinder which Iv provide has the effect of rendering the resistance `on this stroke also more nearly uni- 5form, i. ejmore like that of a dash pot conton, greater at the beginning of this stroke,

but the pressure difference on opposite sides of the piston is less, causing less leakage around the piston, than in any other part of the stroke. The taper which I provide pervmits greater leakage around the piston at this point, where it would ordinarily be least, thus' counteracting the abnormally rapid increase in resistance in that part ofthe stroke, and renderingn the resistance throughout the length of the stroke much more nearly uniform than in the ordinary form of air dash pot. I

Although I have illustrated buttwo slight modiications of structure and mentioned only one application of my device I-do not wish to be understood as limiting it to the specific forms illustrated, nor'to the uses mentioned, as many modifications of structure and use are possiblel to those skilled in the art within thescope of the present invention andthe appended claims.' Y f What I claim is:

l. In combination withmanually operated mechanism: an air dash pot comprising a cylinder having a gradually enlarging internal diameter towards the closed endthereof. e

2. An air dash pot, comprising a piston in a cylinder closed at one end, for use with a manually operated, spring returned mechanism, for limiting the speed of the returning motion caused by said spring, the clearance jaround the piston of said dash pot being varied in such a way that the clearance is greatest Where the force exerted bythe spring is least. y

sisting effect of said dash ypot throughout a partof the return motion.

4. An air dash Ypot comprising a piston in a cylinder which has one end so arranged that air may be compressedbetween it and said piston, and said cylinder having a form in which the internalv diameter increased gradually toward said end thereof.

FREDERICK G. L. BOYER.v 

